Using isotopic and geochemical tracers to identify sources of runoff

Aims and objectives

1. Identify the main sources of water at the catchment scale.
2. Use this information to improve the understanding of the sources and fate of C through the catchment.

How we will use the data

• Precipitation samples: Identify the isotopic signature of precipitation inputs
• Soil water: Identify isotopic signature to monitor mixing of soil water and precipitation and the travel time from soil to the stream.
• Stream sampling (catchment outlet): Detect seasonal trends and allow for the calibration of estimated transit times.

A strong seasonal variation can be seen in the isotopes.

The sources of water (rain, snow and soil water) have distinct signals

There is a large variation between the two slopes

This may be useful for identify and tracing carbon in the system

CDOM is a good suggorate for DOC. There is large daily diurnal variation.

The rainfall event had a dilution effect on DOC.

Soil pH data collected at 14C profile sites.

Willow sites differ greatly from the other sites.

Additional samples were collected along transect 2.

Interesting findings so far

The isotope data looks promising to inform how C is transported through the catchment.

Strongly controlled by active layer dynamics.

Isotopes will be used to inform the hydrological model of the catchment.

Paper Ideas

Linking soil dissolved carbon with stable isotopes to identify sources in Siksik

Outreach

Presentation at EGU 2013

1. Develop a parsimonious hydrological model for an Arctic catchment using hydrological tracers to improve model structure.

1. Use isotope data to estimate transit times in the catchmemt.

2. Improved hydrology and freeze/thaw routines for ECOSSE and improved DOC estimates for parsimonious hydrological model.

Tasks completed

• Developed a coupled hydrology-biogeochemistry model to simulate stream discharge and DOC for Granger catchment.

Hydrological component

• Based on the conceptual HBV model.
• Includes an additional modules:
  • for the affect of slope facing aspects, and
  • freeze-thaw processes do to soil frost and permafrost conditions

DOC component

• Based on the DOC components of the ECOSSE model
• Simplified DOC production and loss functions using
  • a Q10 relationship for temperature, and
  • a soil mositure modifying term.

Subarctic alpine catchment with permafrost on north facing slopes.

Characterised with large spring melt stream discharge events early spring.

Discharge simulations captured the spring melt timing and magnitude for most years.

Simulated discharge is strongly correlated (\(r^2=0.67\)) with observed discharge.

DOC simulations captured the spring melt timing and magnitude for most years with a strong correlation to the observed DOC (\(r^2=0.81\)).

The simulations also indicate that DOC concentrations increase later in the season.

Simulations closely resemble observed trends of both DOC ans stream discharge.

Soil water DOC works well for the south facing slope, but is exported a little quickly on the north facing slope.

Transit times are based on the smoothing of the isotope signal by the catchment

Interesting findings so far

Modelling results so far indicate that conceptual models will work in paermafrost environments

Isotopes should be able to be used to estimate transit times, which will improve hydrological models

Paper Ideas

Evaluation of parsimonious hydrological model of an arctic catchment

Improving the model using hydrological stable isotopes (transit times)

Outreach

Presenting conceptual model at EGU 2014

Submitted manuscript to Hydrological Processes.